Saturday, December 4

Confusion and frustration over outdated but legal earthquake rules


New research shows there are tangled earthquake rules that could lead to homeowners strengthening the wrong parts of buildings or having to pay twice to find out if their floors are safe.

BNZ Harbor Quays Building.

BNZ Harbor Quays Building.
Photo: RNZ / Phil Pennington

Engineers are urging officials to untangle what they call “this confusion,” but there are no signs of that happening.

the investigate for the Ministry of Business, Innovation and Employment (MBIE) compared the two sets of rules for engineers conducting seismic evaluations of commercial buildings.

Not surprisingly, the newer rules have been found to be superior, but unfortunately only the older rules have legal value.

New Zealand has thousands of multi-story buildings with particularly weak types of precast concrete or hollow floors, which have been known for 30 years to be especially risky and suffered extensive damage in the 2016 Kaikōura earthquake, as exemplified at BNZ Harbor. Quays. in Wellington, where the soils cracked and sank.

Cracks in the floor supports of the BNZ Harbor Quays building in Wellington after the 2016 Kaikoura earthquake.

Cracks in the floor supports of the BNZ Harbor Quays building in Wellington after the 2016 Kaikoura earthquake.
Photo: WSP Opus Report.

Researchers have found that the hastily introduced rules manual in 2017, the so-called Red Book, produces overall earthquake ratings (or New Building Standards – NBS) similar to the newer rules created in 2018 in response to Kaikōura.

But it also shows that the older rules are not that good at detecting the weakest parts of a building, especially not for concrete buildings or for floors, which are usually the weakest part.

“This means that the [two approaches] identified different vulnerabilities in buildings, which implies that modifications based on the Red Book may not address the greatest vulnerabilities of a building, “the new report said.

This made a complex situation worse, he said.

The companies “want to know that the modifications address weaknesses in their building that pose a risk to life and safety of people,” but the two sets of guidelines did not build trust.

However, only the Red Book contains the legally binding rules for determining whether a building is prone to earthquakes.

The newer rules (called the Yellow Chapter or Yellow Book) do not carry that weight, although engineers rely on them more.

“There is confusion and frustration for engineers,” said one of the researchers, Dr. Nicholas Brooke, echoing the report’s repeated line that the industry wants the newer, superior Yellow Chapter to prevail.

The confusion could lead to a building owner being forced to conduct an earthquake-prone assessment under the Red Book, and then having to conduct a second assessment under the Yellow Chapter, Brooke told RNZ.

Dr. Nicholas Brooke.

Dr. Nicholas Brooke.
Photo: Supplied

“In some circumstances, it will result in additional and possibly unnecessary cost to building owners.”

Jenni Tipler, MBIE’s manager of performance and building engineering, said they should consider the research findings before deciding whether to incorporate the Yellow Chapter into legislation.

He always had to balance evolving engineering knowledge with the “need to provide certainty for the industry.”

As for modifications, this was independent of evaluating a building’s NBS, he said.

“It is common for additional work to be identified and incorporated as the remediation plan develops.

“Building owners must be confident that, having met the mandatory national requirement, the level of compliance will not change anytime soon.”

He said in a previous statement that he first wants to find out the impacts on “the building system” if what is mandatory was changed.

The ministry has yet to assess these impacts, although the Yellow Chapter was published three years ago.

New research for MBIE says there are already impacts from not making the change, such as building owners being reluctant to conduct a seismic assessment.

“They want to be confident that the modernization work is aligned with any looming regulatory environment.

“They expect the regulation to be based on the latest knowledge,” he said.

Instead, “the businesses and government agencies that vacated the buildings have contributed to this confusion,” doubling down on their health and safety obligations.

Brooke said that in practice, engineers are not using the older Red Book unless it is legally required in situations where the building owner has to formally respond to advice. This was not happening much over the 80s-90s buildings built when flimsy pre-fab floors were a ubiquitous design.

“The industry is making it work quite well, I think, in the sense that the Yellow Book is used for almost everything,” he said.

There are very few Red Book building evaluations.

New Zealand is unusual around the world for the high proportion of commercial and apartment buildings with the weak floor type: more than 60 percent of the commercial floor area in Wellington falls into this category.

Research on how to fix them only began in earnest after the Kaikōura earthquake.

This late start threw structural engineers “in a bad light,” said Brooke and other leading researchers. in 2019.

By mid-2021, it had been established that floors could be “highly vulnerable” and fail in many ways, including “web splitting”, and the floor slab falling off its seat, as happened in House of Statistics in Wellington in the Kaikōura earthquake.

Research by the country’s leading project on the modernization of such floors, ReCast Floors, around the same time revealed key findings:

  • Buildings in Wellington can have undetected network cracks, reducing the load they can bear.
  • Finding out the extent of that decline is difficult
  • Some floor connections (called beta units) can be “highly susceptible to damage”
Researchers at ReCast Floors test a hardened backup system, an upgrade that is now recommended in New Zealand.

Researchers at ReCast Floors test a hardened backup system, an upgrade that is now recommended in New Zealand.
Photo: ReCast Floors Research

As a consequence, the industry is being warned no more buildings with hollow floors, and an industry source told RNZ that advice is being followed.

On the bright side, the ReCast project thinks it has found a pretty good upgrade solution, called a ‘strong backup system’, which it is testing further.

The final results of the project are due to be presented early next year.


www.rnz.co.nz

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